The study of gene expression and its control in eucaryotic cells has required the use of model systems due to the complexity of the eucaryotic cell. One of the most rewarding of such model systems has been infection of human cells by human adenoviruses. This proposal is concerned with advancing our knowledge of the molecular biology of adenoviruses with respect to a very interesting and little understood phenomenon recently observed with eucaryotic cells--that phenomenon is the split nature of eucaryotic genes. Adenovirus was one of the first systems for which such split gene structure and their spliced mRNAs were demonstrated and presents a unique model system with which to study their expression. The overall aim of the proposed research is to establish the first paradigms of the transcription of eucaryotic split genes so that they may be applied to more general systems. My proposed research is designed to study viral late gene transcription with an emphasis on the production of "spliced" RNA. The first objective is to define the structures of the late viral initial transcripts and processed intermediates. This is a continuation of preliminary work which has suggested, but not proven, that spliced RNAs are generated by a postranscriptional event which uses long nuclear RNA as substrate. The second main objective is to detect and isolate a splicing processing activity from virus-infected cells. Several assays have been designed to detect such an activity--both a general assay for use with crude cell extracts and a more specific assay especially designed to detect the production of individual viral spliced mRNAs. During such a purification it is hoped that some insight will be gained into how the processing of RNA is controlled, perhaps through the co-purification of viral modifying factors.